(1) Field of the Invention
The subject of the present invention is an injector that can be used in particular in a device for the combustion of corrosive residues such as those containing halogenated, particularly chlorinated, hydrocarbons.
(2) Description of Related Art
The industrial manufacture of chlorinated organic compounds generates abundant quantities of residue, often containing chlorine. These residues may either be in the gaseous state, as for example in the case of the manufacture of vinyl chloride or of its polymers or copolymers, or in the state of liquid and/or tarry solid, obtained in the manufacture of aliphatic, cycloaliphatic and/or aromatic chlorinated hydrocarbons. The composition of these chlorinated residues varies according to their origin. Certain residues comprise chlorinated tarry products, at least some of the constituents of which contain more than 7 carbon atoms per molecule. Other chlorinated residues comprise chlorinated C4 compounds and/or chlorinated C6 compounds. These chlorinated residues may be accompanied by other compounds comprising chlorinated C1 to C4 constituents. These chlorinated residues may also comprise polychlorinated biphenyls (PCBs) used as dielectric fluids and coolants and which need to be got rid of, given the ban on the use of such products.
One means of solving the problem of the build-up of these residues and of the contamination of the air and/or of the water courses into which they may be discharged, is to burn them at high temperature in a combustion chamber, with the recovery of gaseous hydrochloric acid which can be put into the form of an aqueous solution, and possibly the production of steam.
More specifically, these chlorinated gaseous and/or liquid residues are burned in the presence of excess air and water at temperatures ranging from 900xc2x0 C. to 1450xc2x0 C., and generally between 1200xc2x0 C. and 1300xc2x0 C. in an installation comprising, in particular, a burner into which the chlorinated residues and an oxidizer are injected; said burner being surmounted by a furnace in which the mean residence time of the molecules is at least 3 seconds.
The hot gases leaving the furnace are quenched (rapidly cooled). The HCl formed is absorbed in absorbers, which leads to concentrated (33%) commercial solutions. Any chlorine that might be formed is absorbed in an alkaline aqueous solution.
The burning of these residues is accompanied by lively combustion which can be obtained stably and continuously only in specially designed apparatus. The problem is that the combustion of this type of residue is accompanied by difficulties and problems of various natures: the clogging of the burners and of the injectors particularly when the residues are viscous, difficulties in finding the right settings for obtaining total combustion yielding hydrochloric acid containing only a minimum of free chlorine, together with zero production of carbon, corrosion, swift degradation of the parts of a burner if certain members or walls of the apparatus are not protected with a refractory and/or antiacid coating, or with special arrangements, for example for the injection of a significant volume of cold non-combustible gas around the flame.
Patent application FR 2509016, incorporated by reference into this application, describes a device that can be used in particular for the combustion of halogenated corrosive products or product mixtures or ones likely to generate corrosive products, by bringing said products in the dispersed state into contact with an oxidizing fluid at a high enough temperature to allow the cloud of particles formed to become incandescent.
This device, depicted in FIG. 1, comprises a combustion chamber (7), a head (1) for dispersing the phase that is to be burned into said chamber, a connecting plate (2) connecting said dispersion head to the combustion chamber, fluid inlets (3), (4) and (5), and a deflector (6). Also shown in this FIG. 1 is the pipe (30) for the outlet of the combustion gases, and a blow-out seal (29).
The dispersion head (1) is an essential part of this device. This dispersion head (FIG. 3) comprises:
a device for the axial arrival of the phase that is to be burned and of the auxiliary fluids, or injector (8), fitted with a guide (9),.
a chamber known as a swirl chamber for introducing swirl into a primary fraction of the oxidizing phase (or of the oxidizer), allowing said primary fraction to be introduced into the combustion chamber in the form of a vortex sink flow, to which enough momentum is imparted to, by transferring the momentum, disperse the phase that is to be burned, said swirl chamber comprising a tangential inlet (15) leading said primary fraction of the oxidizing phase into an annular space contained between an external wrapper (16) and an internal wrapper (17) perforated at its upstream part and behaving like a multitude of tangential inlets, said swirl chamber ending in a conical part (18), the end of this conical part (18) and the injector (8) are dimensioned and arranged in such a way as to form a narrow annular passage (references 26 and 27);
an inlet into the combustion chamber of a secondary fraction of the oxidizing phase (21);
a deflector (24) toward the base of the combustion zone, allowing said secondary fraction to be deflected down toward the base of the combustion zone, said deflector delimiting a passage (28) around the combustion zone, the inlet (21) and the deflector (24) being dimensioned and arranged in such a way as to allow the secondary oxidizing fractions to constitute the complement of the oxidizing phase needed for combustion and at the same time to stabilize the incandescent cloud and to cool the deflector and the connecting plate (19), which bears the deflector (24), the shell rings (20), the inlet orifices (21) and the fixing means (22), which can be adjusted during operation with respect to the sole (25) of the combustion chamber;
an annular leakage space (23) formed between the sole (25) and the plate (19), which allows a second part of the secondary fraction of the oxidizing phase to be introduced.
The dimensioning recommended in this document, of the various parts concerned is such that the ratio of the outside diameter (27) to the inside diameter (26) of the narrow annular passage is between 1.1 and 1.6 and preferably between 1.15 and 1.4 and that the ratio of the diameter (28) of the passage left by the deflector to the diameter (27) mentioned hereinabove is between 1.5 and 5 and preferably between 2 and 4.5.
FIG. 2 depicts details of the device for the axial arrival of the phase that is to be burned and of the auxiliary fluids, or injector.
This injector comprises:
a guide (9),
a tube (12) for bringing in the fluid containing the products that are to be burned,
auxiliary coaxial inlets, namely concentric tubes (10), (11) and (12) which, via the annular spaces (13) and (14) allow the top-up fuels and/or oxidizers to be introduced. Altering the geometry of the tube (10) makes it possible also to alter the configuration of the combustion cloud and to fulfill an adjustment function.
Such a device is well suited to the burning of chlorinated residues. The applicant company has used a similar device for burning liquid chlorinated residues.
Thus, for example, the applicant company has used this device for the combustion of residues containing approximately 77% by weight of chlorine. These residues in particular comprise hexachorobutadiene, hexachlorobenzene, tetrachlorobenzene, pentachlorobenzene and hexachloroethane.
This residue is a viscous liquid, the crystallization point of which is higher than 160xc2x0 C.
The complete installation comprises a burner/combustion chamber assembly as depicted in FIGS. 1, 2 and 4. In FIG. 4, which depicts the dispersion head, the shell rings (20) have been omitted and said swirl chamber ends in a frustoconical part (18), the end of this part and the injector (8), the guide (9) of which is shorter, are arranged in such a way as to form a narrow annular passage (references 26 and 27). In this device, the ratio (27)/(26) is 1.28 and the ratio (28)/(27) is 4. The installation also comprises:
a quenching device (not depicted in the figures),
a string of 4 Venturi-type absorbers (not depicted in the figures),
and a neutralizing column (not depicted in the figures).
The depression is created in the combustion chamber by virtue of 4 Venturis in series and an extractor.
The residue, the flow rate of which is 2500 kg/h, is conveyed to the burner by the concentric tube (12). The temperature in the combustion chamber is 1200xc2x0 C. The depression in this chamber is kept at approximately 100 mbar.
2700 Sm3/h of atomization air at 0.5xc3x97105 Pa is introduced through the annular space (27)/(26), that is to say via the tangential inlet (15).
10 Sm3/h of tertiary air is injected via the annular space (14) between the tubes (10) and (11).
An overall secondary-air flow rate of 2500 Sm3/h is made up of a first flow of secondary air drawn in through the holes (21) in the bottom plate (19) and of a second flow of secondary air drawn in through the annular leakage space (23).
The composition of the flue gases leaving the combustion chamber is as follows (percentages by weight):
After these flue gases have been treated in the absorbers, a clear hydrochloric solution is obtained containing 30 wt % HCl.
The Applicant company has found that, although it yielded excellent combustion of said chlorinated residues, this device did, over time, exhibit disadvantages due in particular to the device for the axial arrival of the chlorinated residues to be burned and of the auxiliary fluids or injector depicted in FIG. 2.
What the Applicant company actually found was that the passages in the rings formed by the concentric tubes often became blocked. These blockages led to said injector being changed on average every 30 days.
Because of the expensive material (tantalum) of which these concentric tubes are made, these operations had a serious impact on the budget. These changes took several hours, and also led to costly cooling of the furnace, giving rise to a drop in productivity.
In addition, as the tubes were becoming blocked, the combustion of the chlorinated derivatives was disturbed by a haphazard supply of fluids (fuel and oxidizer), leading to a disruption in the quality of the outfall.
In order to reduce the cost of the operations, the Applicant company modified the nature of the material of which the tubes were made and used ordinary steel.
In addition to the blockages mentioned above, the Applicant company found that the tubes became holed, leading to migration of fluids from one tube to the other.
Another disadvantage observed by the Applicant company was erosion of the xe2x80x9ctipxe2x80x9d or end of the injector, leading to poor atomization of the products to be burned and therefore to poor combustion.